The inflammatory bowel diseases are characterized by pathology associated with abnormal or poorly regulated intestinal immune and inflammatory responses. One of the hallmarks of these diseases is the recruitment and accumulation of lymphocytes and other leukocytes from the blood into affected mucosal tissues.Here the applicants propose to clone and characterize cDNAs encoding the mucosal vascular addresssin (MAd), a 60 kD tissue specific endothelial cell adhesion molecule for lymphocytes that mediates lymphocyte homing to mucosal lymphoid and extralymphoid sites. They will take advantage of their recent identification of a transformed mouse endothelial cell line that can be induced to express high levels of MAd. This cell line will be an excellent source of mRNA for production of libraries containing addressin-encoding cDNAs. Two independent approaches will be undertaken to clone cDNAs encoding the molecule probing gt11 or Zap fusion proteins with specific monoclonal and polyclonal antibodies; and the COS cell expression/immunoselection protocol of Seed adn Aruffo. Confirmation of the identity of cDNAs isolated will involve antigenic and functional analyses of the encoded antigen expressed in transfected COS cells. Addressin-encoding cDNA sequences will be analyzed for homology with known adhesion receptors or other molecules. Longer term goals will include: specifically involved in lymphocyte binding. 2) Analyses of the gene structure and regulatory sequences. They will be particularly interested in defining sequences important to the cytokine regulation and tissue specific expression of the addressin. 3) A high priority will be to use the expressed addressin, either in stable transfectants or as a soluble molecule or immunoglobulin chimera, to define the lymphocyte surface receptors responsible for addressin recognition. 4) Finally, they will isolate human MAd-encoding cCDNAs, allowing extension of studies of this physiologically important cell adhesion molecule to normal and pathological settings in man. The proposed studies should provide insight into the basic molecular mechanisms of lymphocyte homing to mucosal sites. An exciting possibility is that these insights will lead to novel approaches to regulating immune and pathologic inflammatory responses in the gut and other mucosal tissues.